EPZ015866 (GSK591) is a potent selective inhibitor of the arginine methyltransferase PRMT5/MEP50 complex thus stopping the methylation of histone H4 with IC50 of 11 nM. It also maintains superior selectivity against other panels of methyl transferases inhibiting the symmetric arginine methylation of SmD3 with EC50 of 56 nM. MW: 380.5. Purity ≥98% by HPLC